Most engine start devices for starting small, air-cooled gasoline engines mounted on manual work machines, such as bush cutters and chain saws, which have been used increasingly recently, include: a recoil type driving section; a driven section connected to the engine crankshaft via a disconnecting means such as a centrifugal clutch; and a buffer/power storage section disposed between the driving section and driven section, used to buffer the driving force of the driving section, and having a spiral spring or the like for elastically storing power between the driven section and itself. The recoil type driving section has: a recoil reel around which recoil rope is wound; and a recoil spiral spring disposed between the recoil reel and the casing, and fixed to the recoil reel and casing at its inside end and outside end respectively. By manually pulling out the recoil rope, the recoil reel is rotated in one direction and, simultaneously with this, the recoil spiral spring is wound tighter, thereby storing springing force. By releasing the recoil rope from the hand in this state, the power stored in the recoil spiral spring is released and the recoil rope is automatically wound back around the recoil reel.
However, the foregoing recoil type driving section requires the recoil rope to be pulled out every time the engine starts. Generally, the recoil rope must be pulled out quickly with one long stroke. The elderly people, those who are not physically strong, or people working in narrow spaces, may not be able to start the engine by pulling out the recoil rope only one time. In view of such drawbacks, there have been proposed many techniques for facilitating engine-starting operation by pulling recoil rope. Some of these have been practical to use. However, problems of inconvenience in pulling out the recoil rope still remain. On other hand, the recent development of small-sized electric motors and batteries is remarkable as they are extremely compact and have a large capacity.
In order to avoid the inconvenient operation of a recoil type start device described above, in addition to such a recent circumstance, an electric engine start device capable of easily and reliably starting the engine by the operation of a simple switch is reviewed, and further development of this type of engine start device is in demand. This type of electric, start device for small-sized engine was proposed many years ago as disclosed in Japanese Utility Model Laid-Open Publication No. 63-110672 (patent document 1). An electric start device disclosed recently is in, for example, Japanese Patent Laid-Open Publication No. 2002-285940 (patent document 2).
The start device in Japanese Utility Model Application Laid-Open No. 63-110672 includes: a DC motor driven by power supplied by a battery; a spiral spring wound up by a spring barrel driven by worm gear fixed to the output shaft of the motor; an output rotation shaft to which the inside end of the spiral spring is fixed; an engine rotation shaft connected to the output rotation shaft via a one-way clutch; a rotation lever for stopping the rotation of the output rotation shaft or for canceling the stop; a synchronizing electrical switch turned on only when the lever cancels the stop of the rotation of the output rotation shaft; and an armature current control circuit designed so that when the electric switch is turned off, the motor is driven, so that when the motor exceeds a set rotating speed, the rotation is continued to wind up the spiral spring, and so that when the spiral spring has been fully wound up and the motor consequently decreases below the set rotating speed, the supply of power and hence the rotation of the motor are stopped.
Further, the basic configuration of the start device in Japanese Patent Laid-Open Publication No. 2002-285940 (patent document 2) is substantially the same as that in the patent document 1, except that the driving side is provided with a known recoil type driving section in addition to the electric motor mentioned above. In other words, the start device in the patent document 2 is just a combination of the start device in the patent document 1 and the known recoil mechanism.
On the other hand, Japanese Patent Publication No. 2573340 (patent document 3) has disclosed a spiral spring type start device accommodating in a single frame: a battery; a DC electric motor driven by the electric power of the battery; a control device for stopping the operation of the motor; a high reduction ratio speed reduction mechanism for transmitting the power of the motor; a spiral spring type power storage device driven by the high reduction ratio speed reduction mechanism; and a power transmission device for transmitting the power in the power storage device to the crank shaft in one direction. The high reduction ratio speed reduction mechanism includes: a planetary gear system speed reduction device (in a first stage), which is disposed on an axis parallel to the crankshaft and driven by a DC electric motor; and a speed reduction device (in a second stage), in which a drive gear on the output shaft of the planetary gear system speed reduction device engages with a driven gear disposed integrally on the periphery of the springing power storage chamber of the power storage device.
Additionally, in an engine start device disclosed in, for example, Japanese Utility Model Laid-Open Publication No. 2-13171 (patent document 4), a spring barrel is supported so as to be pivotal in one direction via the supporting system of a planetary gear speed reduction device disposed opposite the engine crankshaft. The spring barrel is controlled so as to be rotated at a speed decreased by the planetary gear speed reduction device connected to the spring barrel via a combination of speed reduction spur gears, which include a large gear and a small gear fixed to the output shaft of the DC electric motor disposed in the housing. In this case, rotation in one direction is made by the engagement of a ratchet pawl with one of the teeth disposed on the periphery of the spring barrel. Disposed on the crankshaft side of the spring barrel are a starting ratchet wheel and a starting ratchet pawl. The ratchet wheel freely rotates when the wheel and pawl disengage from each other. Fitted to the starting ratchet wheel is a start device ratchet wheel, which engages with a centrifugal clutch pawl attached to the crankshaft.
The batteries used as power sources for the engine start devices disclosed in the patent documents 1 to 4 are so-called NiCad batteries or nickel metal hydride batteries. In the patent documents 1 to 4, the places where these batteries are accommodated are not specified, as is apparent from the descriptions above. Usually, such batteries are disposed in start devices as in the patent documents 3 and 4. Otherwise, due to the large volume of the entire of conventional batteries, the batteries are attached to parts specifically provided near the start devices. Further, the batteries are disposed between the engines and starting electric motors. For instance, in order to obtain, from the foregoing batteries, power required for the electric motor to wind up the spiral spring of the power storage device, a large number of NiCad batteries or nickel metal hydride batteries are needed. This limits the potential for reductions in the size and weight of the start devices.
According to the engine start device in the patent document 1, the engagement of the worm gear directly connected to the electric motor with a worm wheel formed on the periphery of the spring barrel rotates the spring barrel in one direction. This prevents reverse rotation of the spring barrel. However, in a power transmission mechanism employing the engagement of the worm gear and worm wheel, the output shaft of the electric motor is disposed perpendicular to the rotating drive shaft of the spring barrel. Such a disposition is not efficient (approximately 60%) in design, leading to an inevitable limit on possible reductions in size. Since the engine start devices in the patent documents 1 and 2 compose their speed reduction mechanisms out of the worms and worm wheels of the spring barrels, it is extremely difficult to make the entire start devices more compact.
In the patent document 3, the high reduction ratio speed reduction mechanism is disposed between the electric motor and the spring barrel, thereby reducing the motor volume and battery volume to 1/10 and 1/6, respectively, of those of a cell start device or below. Accordingly, mounting a storage battery in the start device does not hinder practical use. However, the high reduction ratio speed reduction mechanism sets an extremely high reduction ratio of 1/250 to 1/300. This is because required output torque should be ensured by an electric motor of a small size and small volume and the spiral spring should stably store power. In addition, the patent document 4 disposes the support shafts of the electric motor, spring barrel, small-diameter ratchet wheel, and ratchet pawl parallel to one another. This makes it difficult to make the engine start device more compact.
In view of the drawbacks discussed above, the applicant of the present invention has realized an engine start device ultimately reduced in size and weight by eliminating unnecessary components as in, for example, Japanese Patent Application No. 2005-196419 (patent document 5) proposed in the past by the same applicant, and by a rational design.
The basic configuration of this engine start device is as follows: the engine start device includes: a small-sized electric motor driven by a battery; a power storage section in which the power of the small-sized electric motor is drive-transmitted via a high speed reduction mechanism in the direction of force storage; and a power transmitting section that transmits the power stored in the power storage section to the engine crankshaft. The power storage section has a spring and a rotating support member that supports one end of the spring. The spring may be a spiral spring or coil spring. In the case of the spiral spring, the rotating support member may be composed of a spring barrel and, in the case of the coil spring, a normal gear can be used.
A first gear is formed on the rotating support member. A second gear is fixed to the output shaft of the high speed reduction mechanism. The first and second gears engage with each other. The engine start device has a rotation inhibiting means disposed in the power storage section or power transmitting section. The rotation inhibiting means normally permits the rotation of the power storage section or power transmitting section in the direction of release of power storage, whereas it obstructs the rotation in the direction of release of power accumulation when the electric motor is not operating. The high speed reduction mechanism is a planetary gear system speed reduction mechanism. The rotation axes of the power storage section and power transmitting section are on the same axis as the crankshaft. The rotation shafts of the small-sized electric motor and high speed reduction mechanism are parallel to the crankshaft. The spur gears of the first and second gears are engaged to each other.
This configuration has made it possible for the engine start device in the patent document 5 to overcome the above-described mechanical problems of the start devices for small-sized engine disclosed in the patent documents 1 to 4. However, the engine start device in the patent document 5 has not overcome such problems as how to drive such a small-sized engine-start mechanism smoothly, securely and safely using a compact battery. Specifically, in order to reduce both the size and weight of the entire work machine, the battery that drives the ignition circuit, fuel supply control circuit, etc., of the engine must not only simply start the engine but have a required discharging capacity and reduce the size and weight of the battery itself.
To overcome this problem, in the patent document 5, the engine start device has been developed simultaneously with a battery pack for driving the small-sized electric motor of a start device for small-sized engine as a battery for driving the small-sized electric motor. In addition to high rate lithium secondary batteries, an ordinary self-discharge prevention circuit and an over-current prevention circuit that are connected to the secondary batteries, the battery pack incorporates a protection circuit composed of electronic circuits such as an overcharge prevention circuit, over-discharge restraining circuit, and start switch relay circuit. The battery pack made more compact can be disposed integrally in the switch box of a handle separated from the engine of the manual work machine.    Patent document 1: Japanese Utility Model Laid-Open Publication No. 63-110672    Patent document 2: Japanese Patent Laid-Open Publication No. 2002-285940    Patent document 3: Japanese Patent Publication No. 2573340    Patent document 4: Japanese Utility Model Laid-Open Publication No. 2-13171    Patent document 5: Japanese Patent Application No. 2005-196419